Flexible band devices for converting rotary motion of a drum or a roller into linear motion are well known and are disclosed, for example, in U.S. Pat. No. 3,167,962 issued to D. P. Scotto and U.S. Pat. No. 3,488,098 issued to B. J. Sobczak.
Furthermore, a flexible band device has been incorporated into a magnetic head positioning mechanism as disclosed in U.S. Pat. No. 4,170,146 issued to W. M. Owens. Therein, angular movement of a stepper motor output drum is converted to linear motion of a carriage which carries a magnetic head along a diameter of a flexible record disk known in the trade as a "floppy disk". The disclosed mechanism has a stainless steel flexible band wrapped around the output drum of the stepper motor with the ends of the band coming off the drum tangentially and aligned with each other. One end of the band has a slot in it through which the other end passes. The ends of the band are attached to the carriage carrying the magnetic head and thereby angular movements of the drum are transmitted to the carriage as linear motion.
The standard floppy disk, which may be a disk of plastic coated with iron-oxide, has a track density of 48 tracks per inch on a recording area approximately 0.729 inches wide. The flexible band-drum connection, because of its construction, limits the drum to one partial revolution of approximately 320 degrees. Within this partial revolution, the drum must move the read/write head across the width of the recording area. Commercially available floppy disk drives utilizing flexible band position devices for positioning of read/write heads over a recording area usually employ a stepper motor having a step angle of 3.6 degrees and an output drum having a circumference of approximately 2 inches and a diameter of 0.66 inches. While such a positioning device provides positioning of the head with the required accuracy, one of its drawbacks is that it is costly because the stepper motor with a 3.6 degree step angle is a relatively expensive item.
Attempts have been made to reduce the cost of flexible band positioning devices by incorporating a less expensive stepper motor. For example, a sheet metal stepper motor which costs approximately two and a half times less than a conventional stepper motor is commercially available and has been considered for use in the flexible band positioning device. The problem however, with the use of a sheet metal stepper motor is that it is not available with a step angle of less than 7.5 degrees. Thus, use of a stepper motor with a 7.5 degree step angle requires an output drum with a circumference of approximately 1 inch and a diameter of 0.33 inches. Wrapping and unwrapping of the metal band around the drum with such a small diameter will introduce stresses in the material which could cause fatigue failure and thus destroy the positioning device.